@stefanpenner the relationship changes were removed from `commitDetails` in [f261dc](https://github.com/emberjs/data/commit/f261dc6b96bb00fe794918a9c840e6bb234b97e4#L0L199). This meant that @ghempton's original PR would not work unless we passed it down to the RESTAdapter. @tjohn and I decided it should be a separate argument as it is conceptually different from `commitDetails`. We are unsure that this is the best solution moving forward, any thoughts?